FIG. 9 is a cross-sectional view of a known magnetic sensing element (spin-valve thin film element) taken in a direction parallel to a surface opposing a recording medium.
The magnetic sensing element shown in FIG. 9 includes a Ta underlayer 1 and a seed layer 2 made of a metal having a bcc (body-centered cubic) structure, such as Cr, on the underlayer 1.
The seed layer 2 underlies a multilayer composite T1 formed by depositing an antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, a free magnetic layer 6, and a protective layer 7, in that order.
The protective layer 7 is formed of Ta; the free magnetic layer 6 is formed of NiFe; the nonmagnetic material layer 5 is formed of Cu; the pinned magnetic layer 4 is formed of a Heusler alloy, such as Co2MnGe; and the antiferromagnetic layer 3 is formed of PtMn.
The multilayer composite T1 has electrode layers 10 on its top and bottom which apply a sense current in a direction perpendicular to the layers of the multilayer composite.
The magnetization of the pinned magnetic layer 4 is fixed in the height direction (Y direction) by an exchange coupling magnetic field generated between the antiferromagnetic layer 3 and the pinned magnetic layer 4.
A hard bias layer 8 made of a hard magnetic material, such as CoPt, is disposed on each side of the free magnetic layer 6. The upper and lower surfaces and sides of the hard bias layer 8 are insulated by an insulating layer 9. The magnetization of the free magnetic layer 3 is oriented in the track width direction (X direction) by a longitudinal bias magnetic field from the hard bias layer 8.
When an external magnetic field is applied to the magnetic sensing element shown in FIG. 9, the direction of the magnetization of the free magnetic layer 3 is changed relative to the magnetization direction of the pinned magnetic layer 5, so that the resistance of the multilayer composite is varied. If a constant sense current flows, the external magnetic field can be detected by measuring a change in voltage resulting from the variation in resistance.
Magnetic sensing elements including a pinned magnetic layer made of a Heusler alloy have been disclosed in Japanese Unexamined Patent Application Publication Nos. 2003-309305 and 2002-319722.
Japanese Unexamined Patent Application Publication No. 2003-309305 has disclosed a pinned magnetic layer made of a Heusler alloy, such as a CoMnGe alloy. However, the magnetostriction and coercive force of the CoMn-based alloys are low. A more suitable material with a high uniaxial anisotropy is desirable for the pinned magnetic layer.
Japanese Unexamined Patent Application Publication No. 2002-319722 has disclosed a tunneling magnetic sensing element including a free magnetic layer and a pinned magnetic layer that are made of a Heusler alloy.
This magnetic sensing element is a tunneling magnetoresistive element (TMR), however, in which the free magnetic layer and the pinned magnetic layer are separated by an insulating material layer (hereinafter referred to as a barrier layer) through which electrons are transmitted by tunneling. Thus, this magnetic sensing element is different from spin-valve GMR elements as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-309305.
The electrical resistance of a TMR element depends on the transition probability of the quantum mechanical states of electrons present at both sides of the barrier layer and the probability of the existence of electrons at both sides of the barrier layer. More specifically, when the potential energy of the barrier layer is represented by V and the states of the electrons at both sides of the barrier layer are represented by <k′| and |k> (according to a Dirac bracket notation), <k′|V|k> is proportional to the transition probability.
On the other hand, in spin-valve GMR elements, a free magnetic layer and a pinned magnetic layer are stacked with a nonmagnetic conductive material layer therebetween, and conduction electrons flow in a direction perpendicular to the surfaces of those layers. Therefore, changes in classical mean free path of up-spin conduction electrons and down-spin conduction electrons are important.
TMR elements and spin-valve GMR elements significantly differ from each other in the mechanisms of the magnetoresistive effect.